With increase in power of an internal combustion engine, in a piston, a piston cooling device, which supplies a cooling oil injected from an oil jet to an annular cooling passage provided in the piston so as to cool a piston head having a piston top face in contact with a combustion gas, is well known.
For example, in a piston cooling device disclosed in Patent Literature 1, a cooling efficiency is improved by providing a guide portion which guides an oil injected from an oil jet to a circumferential passage of a cooling passage in a piston.
Also, at the time of high speed revolution of the internal combustion engine, if a speed of the piston in reciprocating motion becomes greater than that of the oil injected from the oil jet, a period during which the oil is not supplied to the cooling passage in the piston occurs. For this reason, a piston cooling device, which changes an injection speed of the oil injected from the oil jet so as to prevent an occurrence of the period during which the oil is not supplied to the cooling passage, is well known (for example, see Patent Literature 2).